1. Field of the Invention
This invention relates to a barrier rib composition for a plasma display panel and more particularly to a barrier rib composition for a plasma display panel that is adapted to have a high molding property at a low pressure.
2. Description of the Related Art
As shown in FIG. 1, a conventional plasma display panel of alternating current driving system (hereinafter, AC-system PDP) includes a lower glass substrate 10 mounted with an address electrode 12, and an upper glass substrate 20 mounted with a transparent electrode pair 22. A desired thickness of lower dielectric thick film 14 for forming a wall charge and a barrier rib 16 for dividing discharge cells are sequentially formed on the lower glass substrate 10 mounted with the address electrode 12. A desired thickness of fluorescent film 18 is coated on the surface of the lower dielectric thick film 14 and the wall surface of the barrier rib 16. This fluorescent film 18 is radiated by an ultraviolet ray generated during the plasma discharge to generate a visible light. Meanwhile, an upper dielectric thick film 24 and a protective film 26 are sequentially formed on the bottom surface of the upper glass substrate 20 mounted with the transparent electrode pair 22. The upper dielectric thick film 24 forms a wall charge like the lower dielectric thick film 14, and the protective film 26 protects the upper dielectric thick film 24 from an impact of a gas ion during the plasma discharge. Such an AC-system PDP has discharge cells formed by isolating the lower and upper glass substrates 14 and 16 through the barrier rib 8. He+Xe mixture gas or Ne+Xe mixture gas is sealed into the discharge cells.
The barrier rib has more and more made into a high detailed shape in accordance with a tendency to apply a PDP to a high-resolution display. In other words, since a space become smaller as a resolution of the panel increases, it is necessary to form the barrier rib at a high level so as to improve the efficiency. Accordingly, the barrier rib requires a high aspect ratio having a narrow width and a great height. In order to meet such a requirement, there has been suggested the low temperature co-fired ceramic on metal(LTCCM) system that is capable of simplifying the process as well as fabricating a high detailed barrier rib having a high aspect ratio.
Referring to FIGS. 2A to 2F, there is shown a method of fabricating a barrier rib according to the conventional LTCCM system step by step. First, a green sheet 30 is formed. Barrier rib material slurry is prepared in the first process. The barrier rib material slurry is prepared by mixing a barrier rib composition at a component ratio as indicated in the following Table:
TABLE 1 Barrier Rib Composition and Component Ratio Composition Component Ratio (weight %) Glass Powder 70 Solvent 24 Plasticizer 2 Binder 3 Additive 1
wherein the component ratio is calculated assuming that a weight of glass be 100 weight %. As seen from the Table 1, the conventional barrier rib composition contains 70 weight % glass powder, 24 weight % solvent, 2 weight % plasticizer, 3 weight % binder and 1 weight % additive. The barrier rib material slurry is prepared by mixing the barrier rib composition at a component ratio in the Table 1. The barrier rib composition keeps a liquid state and is used for a tape casting.
Such a barrier rib composition is largely divided into an inorganic substance and an organic substance. The glass powder corresponds to the inorganic substance while the solvent, the plasticizer, the binder and the additive correspond to the organic substance. A function of the organic substance will be described in detail. The binder binds the glass powder and keeps a viscosity of the glass powder. Poly-Vinyl-Butyral(PVB) is used as the binder. The plasticizer prevents the green sheet 30 from being hardened easily to give certain flexibility to the green sheet 30. Butyl-Benzyl-Pthalate(BBP) is used as the plasticizer. The solvent is responsible for melting the binder and the plasticizer. Ethanol or Methyl-Ethyl-Ketone(MEK) is used as the solvent. The additive includes a dispersant and a surfactant so as to prevent a conglomeration of the powder. Fish oil is used as the additive.
Meanwhile, an organic substance component ratio of the barrier rib is indicated in the following Table:
TABLE 2 Organic Substance Component Ratio of Barrier Rib Composition Component Ratio (weight %) Solvent 82 Plasticizer 6 Binder 9 Additive 3
wherein the component ratio is calculated assuming that a weight of the organic substance be 100 weight %. As seen from the Table 2, the organic substance of the conventional barrier rib contains 82 weight % solvent, 6 weight % plasticizer, 9 weight % binder and 3 weight % additive.
In the second process, a desired thickness of green sheet 30 is prepared by putting the barrier rib material slurry into a tape casting device(not shown). The green sheet 30 prepared by such a process is shown in FIG. 2A.
Next, the green sheet 30 is disposed on a substrate 32. The green sheet 30 is deposited on the upper part of the substrate 32 having a desired thickness(e.g., 0.5 mm). The substrate 32 is made from glass, glass-ceramic, ceramic and metal, etc. Particularly, Titanium having a thickness of 0.5 mm to 1 mm is mainly used as the metal. The green sheet 30 disposed on the upper part of the substrate 32 is shown in FIG. 2B.
Subsequently, an electrode 36 is formed on the green sheet 30. The electrode 36 is formed by putting the green sheet 30 deposited on the substrate 32 into a printer(not shown). The electrode 36 formed on the upper part of the green sheet 30 is shown in FIG. 2C.
Next, an electrode protective layer 34 is formed on the upper part of the electrode 36. The electrode protective layer 34 protects the electrode 36 from a sputtering caused by the discharge, and accumulates an electric charge produced by the discharge to lower a driving voltage. The electrode protective layer 34 formed on the upper part of the electrode 36 is shown in FIG. 2D.
Finally, a barrier rib 40 is formed by positioning a mold 38 with a shape of barrier rib on the upper part of the substrate 32 and then applying a desired pressure thereto. The barrier rib 40 is molded at the green sheet 30 by positioning the mold 38 having a hole 38a in a shape of barrier rib on the upper part of the substrate 32 and then applying a desired pressure thereto. In this case, a pressing is made between the mold 38 and the substrate 32, or a desired pressure is applied by means of a roller and the like. At this time, the green sheet 30 is moved into the hole 38a for a formation of the barrier rib by a pressure applied to the mold 38 and is molded into a shape of barrier rib. For instance, a pressure of 130 kgf/cm.sup.2 is applied in the molding process. This results from a fact that a barrier rib having a size intended by a manufacturer can not be made until a hardening is rapidly progressed by a component ratio of the green sheet 30 so as to apply a high pressure. The process of molding the barrier rib is shown in FIG. 2E. Also, the barrier rib 40 in which a molding is completed is plasticized at a desired temperature. The barrier rib 40 formed by the plasticization is shown in FIG. 2F.
As described above, the prior art has a problem in that, since a deformation of the substrate is caused when a high pressure is applied to form the barrier rib, a performance of the PDP is deteriorated. Thus, it is necessary to provide a barrier rib composition having an excellent molding property at a low pressure.